Recent evidence has indicated an uncertainty of the best means of management for unruptured brain arteriovenous malformations (BAVMs), whether by medical management or invasive therapy. A Randomized trial of Unruptured Brain AVMs (ARUBA) is proposed in a reapplication, conducted by two independent but highly coordinated units, ARUBA-CLIN and ARUBA-STAT. Patients will be randomized to medical management or invasive therapy (endovascular, neurosurgical, or radiosurgery, alone or in combination) and followed for a minimum of 5 years. The primary hypothesis is that medical management improves long-term outcomes of patients with unruptured BAVMs compared to invasive therapy. There are three associated specific aims: Specific Aim 1.1 a To determine whether medical management is superior to invasive therapy for preventing the composite outcome of death from any cause or stroke (hemorrhage or infarction confirmed by imaging) in the treatment of unruptured BAVMs. Specific Aim 1.1 b If medical management is not superior to invasive therapy, to determine whether medical management is not inferior to invasive therapy for preventing the composite outcome of death from any cause or stroke (hemorrhage or infarction confirmed by imaging) in the treatment of unruptured BAVMs. Specific Aim 1.2 To determine whether treatment of unruptured BAVMs by medical management decreases the risk of death or clinical impairment (Rankin Score >2) at 5 years post-randomization compared to invasive therapy. ARUBA-CLIN will coordinate the day-to-day conduct of the trial and interface with a European unit. It will handle pre-randomization inquiries and respond to clinical queries and policy issues that arise. A Steering Committee of ARUBA-CLIN/STAT investigators and senior coordinators will meet under specified and controlled communication protocols to implement procedures in response to trial needs. The ARUBA-STAT document outlines the overall objectives of the trial, its significance, investigators, sample size calculations, patient randomization procedures, endpoint definition and measurement, the analytical plan, electronic data capture system, quality assurance, and organizational structure of the trial. We have made every effort to avoid duplication between the two proposals, but some overlap seems unavoidable, for which we apologize.